<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>浮动塌陷</title>
  <style>
    .parent{
      width: 800px;
      background: antiquewhite;
      border: 1px solid red;
    }
    .child1{
      float: left;
      width: 200px;
      height: 100px;
      background-color: #005971;
    }
    .child2{
      float: left;
      height: 120px;
      width: 300px;
      background-color: #002183;
    }
    .next{
      height: 150px;
      width: 100%;
      background-color: burlywood;
    }
  </style>
</head>
<body>
  <div class="parent">
    <div class="child1"></div>
    <div class="child2"></div>
  </div>
  <div class="next"></div>
</body>
</html>